(a) Field of the Invention
This invention relates to a method of producing a heat treating furnace member, particularly, to a method of producing a high density and high strength silicon carbide body for a heat treatment furnace used in the manufacture of a semiconductor device.
(b) Description of the Prior Art
It has been customary to produce a member of a heat treating furnace used in the manufacture of a semiconductor device, particularly, a silicon carbide process tube for a diffusion furnace, as follows. In the first step, a mixture of a SiC powder and a carbon powder is kneaded with a binder added thereto, followed by granulating and subsequently drying the kneaded mixture. The resultant dry grains are preformed into a desired shape by, for example, rubber pressing, followed by evaporating the binder so as to obtain a porous preform. The preform is purified with, for example, a halogen gas. Finally, the purified preform is immersed in a molten silicon bath to form silicon carbide by the reaction between the carbon contained in the preform and the silicon in the molten silicon bath, thereby producing, for example, a silicon carbide process tube for a diffusion furnace.
In the prior art described above, however, rubber pressing is employed for preforming the raw material, with the result that the carbon powder is not dispersed sufficiently uniformly in the preform. Naturally, a dense SiC structure is selectively formed in the subsequent step of immersing the preform in the molten silicon bath in only the regions where the carbon powder is concentrated, with the pores of the preform being simply filled with silicon in the regions where the carbon powder is not dispersed. The situation is shown in FIG. 1. It is seen that the raw material SiC particles 2 and the SiC particles 3 formed by the reaction are locally dispersed in the silicon base 1. It follows that the produced process tube fails to exhibit a sufficiently high density and high mechanical strength. Where the material of a heat treatment furnace has a low density and a low mechanical strength, the durability of the material itself is impaired. In addition, bad influences will be exerted on the quality and characteristics of, for example, a semiconductor wafer which is treated in such a furnace.